Traitor is a bit meh of an idea. I’ve had this happen in WOW more than once. Someone gets there account hacked (my own twice, and I tell you a 12 character password and that stupid keychain auth did NOTHING to help) If it’s someone who has access then bank items go missing, our leader was hacked once and bank logs went bye bye, and your alt is left running around trying to sell gold.

Keran is is on the money. There is someone in the Guild stealing stuff and wiping records. So far the only KNOWN case is food theft. Either more has been stolen (and not noticed), or more could easily be stolen (by the same or a different guy).
This is how most corruption scandals start.